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Abstract. Anaerobic digestion (AD) is a promising technology to produce renewable energy from organic wastes and achieve desirable solids reduction. One critical step for the successful and continuous operation of an AD system is the digester start-up, in which fresh feedstock is added periodically to the digester with a portion of finished materials discharged simultaneously, until reaching a steady state. This process is identified as a sequential batch AD process. Currently, the start-up and optimization of operating such a digester is largely determined by trial and error based on several months‘ continuous monitoring and adjustment by experienced operators. This research proposes a novel mathematical model to predict outputs per unit volume of a sequential batch AD process during the start-up phase as well as at steady state. Important model inputs included the feedstock total solids content, inoculum recycle rate, water supplementation, feedstock degradation rate, and methane yield. The model predicted the total methane yield, final end material TS, VS contents, and mass quantity at the steady state. This model provides a useful method for the design, operation, and optimization of large scale AD digesters.